1. Field of the Invention
The present invention relates to a display device for displaying images and, more particularly, to a deflection correction circuit used in a display device and to a phase-locked loop circuit used in the deflection correction circuit.
2. Description of the Related Art
In recent years, display devices interfaced with computers in use have tended to have wide viewing screens with flat faces. In addition, it is a recent trend that display devices require many kinds of and delicate corrections on the viewing screen. However, the prior art deflection correction circuit is unable to satisfy these requirements because complex processing is necessary for such delicate corrections.
The prior art deflection correction circuit is described by referring to FIG. 1. In the prior art deflection correction circuit indicated by numeral 600, an analog calculator circuit 601 generates a distortion-correcting signal 106 for correcting a distortion of an image on the viewing screen. Practically, addition and multiplication are performed by the use of electrical currents in the analog calculator circuit 601 to generate the distortion-correcting signal. With this structure, the deflection correction circuit 600 cannot process complex waveforms, such as square waves and biquadratic waves in spite of the fact that complex processing is required for the delicate correction on a wide screen. Furthermore, the results of processing are easily affected from external factors and so it is difficult to accurately correct the distortion on the viewing screen.
In view of the prior art deflection correction circuit constructed as described above, it is an object of the present invention to provide a deflection correction circuit which is capable of processing complex waveforms, such as square waves and biquadratic waves, without being affected from external factors.
To achieve this object, the present invention provides the following phase-locked loop circuit, deflection correction circuit, and display device.
The present invention provides a phase-locked loop (PLL) circuit having a phase comparator circuit, a filter, and a voltage-controlled oscillator that are connected in series in this order. The output from the voltage-controlled oscillator is fed back to the phase comparator circuit. This PLL circuit is characterized in that it is equipped with a period-detecting circuit and a frequency divider circuit. The period-detecting circuit detects the period of an externally applied signal. The frequency divider circuit divides down the frequency of the output from the voltage-controlled oscillator according to the period detected by the frequency detection circuit and feeds a signal of the resulting frequency back to the voltage-controlled oscillator.
The present invention also provides a deflection correction circuit equipped with a phase-locked loop circuit for feeding the output from a voltage-controlled oscillator back to a phase comparator circuit, the deflection correction circuit acting to produce a distortion-correcting signal for correcting distortions on the viewing screen of a display device and a horizontal drive signal for controlling scan across the viewing screen in response to an externally applied horizontal synchronizing signal. The deflection correction circuit is characterized in that it comprises a period-detecting circuit for detecting the period of the horizontal synchronizing signal, a frequency divider circuit for dividing down the frequency of the output from the voltage-controlled oscillator according to the period detected by the period-detecting circuit, and a digital signal processor for producing a distortion-correcting signal according to the output from the voltage-controlled oscillator.
Furthermore, the present invention provides a deflection correction circuit equipped with a phase-locked loop circuit for feeding the output from a voltage-controlled oscillator back to a phase comparator circuit, the deflection correction circuit acting to produce a distortion-correcting signal for correcting distortions on the viewing screen of a display device and a horizontal drive signal for controlling scan across the viewing screen in response to an externally applied horizontal synchronizing signal. This deflection correction circuit is characterized in that it comprises a period-detecting circuit for detecting the period of the horizontal synchronizing signal, a transient response circuit for dividing the period detected by the period-detecting circuit into subperiods each having a predetermined time and producing such subperiods at regular intervals of time, a frequency divider circuit for dividing down the frequency of the output from the voltage-controlled oscillator according to the subperiods delivered from the transient response circuit, and a digital signal processor for producing a distortion-correcting signal according to the output from the voltage-controlled oscillator.
In addition, the present invention provides a deflection correction circuit equipped with a phase-locked loop circuit for feeding the output from a voltage-controlled oscillator back to a phase comparator circuit, the deflection correction circuit acting to produce a distortion-correcting signal for correcting distortions on the viewing screen of a display device and a horizontal drive signal for controlling scan across the viewing screen in response to an externally applied horizontal synchronizing signal. This deflection correction circuit is characterized in that it comprises a period-detecting circuit for detecting the period of the horizontal synchronizing signal, a digital signal processor for producing distortion-correcting signal according to the output from the voltage-controlled oscillator, dividing the period detected by the period-detecting circuit into subperiods each having a predetermined time and producing the subperiods at regular intervals of time, and a frequency divider circuit for dividing down the frequency of the output from the voltage-controlled oscillator according to the subperiods delivered from the digital signal processor.
Preferably, these deflection correction circuits are further equipped with a phase control circuit for producing a horizontal drive signal according to the output from the voltage-controlled oscillator and the output from the frequency divider circuit.
Further, the invention provides a display device equipped with any one of the deflection correction circuits described above.
Other objects and features of the invention will appear in the course of the description thereof, which follows.